Abstract

The modifications of the G3, G3X, G3(MP2), and G3X(MP2) methods with the aim of providing a better description for the thermochemistry of radicals were developed and assessed. Thus, the RAD modifications not only affect the results for radicals but also affect the calculated heats of formation for closed-shell molecules because these were determined using atomization energies that involve the open-shell atoms. In particular, the RAD procedures were assessed using the G2/97 test set. It was found that the modified procedures all perform better than their standard G3-type counterparts.